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cabling is significantly robust to minimize crosstalk from multiple disturbers. This type of
characterization is necessary to ensure cabling compatibility with applications that utilize all four
pairs for transmitting and receiving signals simultaneously such as 1000BASE-T and applications
that are sensitive to alien crosstalk such as 10GBASE-T.
Propagation Delay & Delay Skew: Propagation delay is the amount of time that passes between
when a signal is transmitted and when it is received at the opposite end of a cabling channel. The
effect is akin to the delay in time between when lightning strikes and thunder is heard - except that
electrical signals travel much faster than sound. Delay skew is the difference between the arrival
times of the pair with the least delay and the pair with the most delay. Transmission errors that are
associated with excessive delay and delay skew include increased jitter and bit error rates.
Return Loss: Return loss is a measure of the signal reflections occurring along a transmission line
and is related to impedance mismatches that are present throughout a cabling channel. Because
emerging applications such as 1000BASE-T and 10GBASE-T rely on full duplex transmission
encoding schemes (transmit and receive signals are superimposed over the same conductor pair),
they are sensitive to errors that may result from marginal return loss performance.
Transfer Impedance: Shield effectiveness characterizes the ability of screened (F/UTP) and fully-
shielded (S/FTP) cables and connecting hardware to maximize immunity from outside noise
sources and minimize radiated emissions. Transfer impedance is a measure of shield effectiveness;
lower transfer impedance values correlate to better shield effectiveness
End Point Connections
End point devices such as access control card readers and panels often use wiring standards which were
developed before Ethernet cabling. Examples include:
RS-485: TIA standard 485, defines the electrical characteristics of drivers and receivers for use in
balanced digital multipoint systems. Digital communications networks implementing the TIA-485
standard can be used effectively over long distances and in electrically noisy environments.
Multiple receivers may be connected to such a network in a linear, multi-drop configuration. These
characteristics make such networks useful in industrial environments and similar applications. TIA
485 enables the configuration of inexpensive local networks and multi-drop communications links,
offering data transmission speeds of 35 Mbit/s up to 10 m and 100 Kbit/s at 1200 m. Since it uses
a differential balanced line over twisted pair, it can span relatively large distances (up to 4,000 feet
(1,200 m)). A rule of thumb is that the speed in bit/s multiplied by the length in meters should not
RS-232C: This is the designation for a series of standards for serial binary single-ended data and
control signals commonly used in computer serial ports defined in TIA standard 232-F, Interface
Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial
Binary Data Interchange, issued in 1997. The standard defines the electrical characteristics and
timing of signals, the meaning of signals, and the physical size and pinout of connectors. An RS-
232 port was once a standard feature of a personal computer for connections to modems, printers,
mice, data storage, uninterruptible power supplies, and other peripheral devices. However, the low
transmission speed, large voltage swing, and large standard connectors motivated development of
the universal serial bus, which has displaced RS-232 from most of its peripheral interface roles.
Many modern personal computers have no RS-232 ports and must use an external converter to
connect to older peripherals. Some RS-232 devices are still found, especially in industrial machines
or scientific instruments.
Current Loop: For digital serial communications, a current loop is an interface that uses current
instead of voltage for signaling. Current loops can be used over moderately long distances (tens of
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